The most accurate method for performing analog signal processing in MOS
(metal-oxide-semiconductor) integrated circuits is through the use of switched-capacitor
circuits. A switched-capacitor circuit operates as a discrete-time signal
processor. These circuits have been used in a variety of applications, such as
filters, gain stages, voltage-controlled oscillators, and modulators.
A switched-capacitor circuit contains operational amplifiers (opamps), capacitators,
switches, and a clock generator. Capacitors are used to define the state
variables of a system. They store charges for a defined time interval, and determine
the state variables as voltage differences. Switches are used to direct
the flow of charges and to enable the charging and discharging of capacitors.
Nonoverlapping clock signals control the switches and allow charge transfer between
the capacitors. Opamps are used in order to perform high-accuracy charge
transfer from one capacitor to another.
The goal of this research is to design and explore future low-voltage switched-capacitor
circuits, which are crucial for portable devices. Low-voltage operation
is needed for two reasons: making reliable and accurate systems compatible with
the submicron CMOS technology and reducing power consumption of the digital
circuits.
To this end, three different switched-capacitor integrators are proposed, which
function with very low supply voltages. One of these configurations is used to
design a lowpass ����� modulator for digital-audio applications. This modulator
is fabricated and tested demonstrating 80 dB dynamic range with a 1-V supply
voltage.
The second part of this research is to show that these low-voltage circuits are
suitable for modern wireless communication applications, where the clock and
signal frequencies are very high.
This part of the research has focused on bandpass analog-to-digital converters.
Bandpass analog-to-digital converters are among the key components in
wireless communication systems. They are used to digitize the received analog
signal at an intermediate center frequency. Such converters are used for digital
FM or AM radio applications and for portable communication devices, such as
cellular phones. The main block, in these converters, is the resonator, which is
tuned to a particular center frequency. A resonator must be designed such that
it has a sharp peak at a specific center frequency. However, because of circuit
imperfections, the resonant peak gain and/or the center frequency are degraded
in existing architectures.
Two novel switched-capacitor resonators were invented during the second
part of this research. These resonators demonstrate superior performance as
compared to previous architectures. A fourth-order low-voltage bandpass �����
modulator, using one of these resonators, has been designed. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32625 |
| Date | 07 December 2001 |
| Creators | Keskin, Mustafa |
| Contributors | Temes, Gabor C., Moon, Un-Ku |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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